Heretofore, improvement in reinforcing characteristics has been needed for a thin sheet used for structures such as an automobile and a household electrical appliance, to achieve prevention of deformation by external stresses.
For example, reinforcement of a steel plate has been proposed as follows (for example, Patent Document 1 below). A steel plate reinforcement sheet is obtained by preparing a steel plate reinforcement resin composition containing epoxy resin, acrylonitrile-butadiene rubber, a curing agent, and a foaming agent; rolling the prepared resin composition to mold a resin layer; and then laminating a reinforcement layer onto the resin layer. Then, the steel plate reinforcement sheet is adhesively bonded to a steel plate, and foamed and cured so that the steel plate is reinforced.
Additionally, use of a thin sheet for automobiles or household electrical appliances involves generation of vibration sound, and therefore improvement in vibration-damping characteristics is also needed for the thin sheet in order to prevent the generation of such vibration sound.
Thus, to improve both of the reinforcing characteristics and vibration-damping characteristics, there has been proposed a foaming thermosetting resin sheet in which three layers are laminated in order, the three layers being a spacer layer containing a liquid epoxy resin, a methacrylic resin, and a curing agent; a vibration-damping material sheet layer containing butyl rubber; and a metal sheet (for example, Patent Document 2 below). By adhesively bonding the foaming thermosetting resin sheet to a thin sheet, the spacer layer works to improve the reinforcing characteristics (rigidity), and the vibration-damping material sheet layer works to improve the vibration-damping characteristics.    Patent Document 1: Japanese Unexamined Patent Publication No. 2005-139218    Patent Document 2: Japanese Unexamined Patent Publication No. H6-170997